It’s been 45 years since George Romney committed one of the greatest gaffes in American political history — a misstep that supposedly inspired one of the most devastating putdowns in American political history.

Romney’s gaffe, which effectively destroyed his run for the presidency before it officially began, came in an interview taped on August 31, 1967, and aired September 4, 1967, on a Detroit television station.

In the interview, Romney, then governor of Michigan and a presumptive Republican candidate for president, referred to his visit to South Vietnam in 1965 and declared:

“You know, when I came back from Vietnam, I’d just had the greatest brainwashing that anybody could get. … Well, not only by the generals but by the diplomatic corps over there. They do a very thorough job.”

The assertion that he had been duped into supporting America’s war effort in Vietnam revealed Romney’s muddled thinking and an uncertain command of foreign policy. (“Could the country afford a President who was so easily deceived?” the New York Times wondered.)

Forty-five years on, Romney’s comment remains striking both for clumsiness and self-destructiveness. And it’s been recalled not infrequently in recent months as Romney’s son, Mitt, has campaigned for the presidency.

When it is recalled, the “brainwashing” gaffe often is coupled with the stiletto-like rejoinder attributed to Eugene McCarthy, then a second-term U.S. senator from Minnesota.

McCarthy supposedly said that rather than brainwashing, “a light rinse” would have sufficed in Romney’s case.

There is no question about Romney’s having made the “brainwashing” claim; this YouTube video cuts to the money quote:

The anecdote’s memorable quality lies not only in Romney’s befuddled claim but also in McCarthy’s “light rinse” quip. Indeed, McCarthy’s retort is said to have been so powerful that it “essentially finished Romney.”

But the precise context of McCarthy’s “light rinse” zinger is at best unclear. My research has turned up no unambiguous documentation about when McCarthy made the comment, where, and specifically to whom.

(And why does this matter? Getting it right matters a lot, especially about an insult so piercing and effective that it lives on like few others in American political lore.)

A database search of leading U.S. newspapers — including the New York Times, the Washington Post, Chicago Tribune, Los Angeles Times, and Baltimore Sun — turned up no published reference to McCarthy’s “light rinse” remark in 1967 or 1968, or for many years afterward.

The nearest contemporaneous hint to a “light rinse” came in a commentary published in mid-September 1967 in the Los Angeles Times, in which conservative columnist James J. Kilpatrick said of Romney:

“Brainwashed, was he? It couldn’t have been much of a laundry bill.”

Kilpatrick’s column did not mention McCarthy, who wasn’t prominently in the news in September 1967. McCarthy did not announce his candidacy for president until November that year.

The first reference found in the database search to the “light rinse” comment was in a commentary written by Fred Barnes and published in Baltimore Sun in April 1983. Barnes’ commentary, however, did not say when, where, or to whom McCarthy uttered the “light rinse” line.

American Melodrama, which was written by Lewis Chester, Godfrey Hodgson, and Bruce Page, described McCarthy’s remark as off-handed and said his aides persuaded journalists to hush it up.

According to American Melodrama, McCarthy was asked “by reporters whether he thought Romney’s ‘brainwashed’ gaffe had dealt the death blow to his chances.”

McCarthy was quoted as saying in reply:

“Well . . . er no, not really. Anyway, I think in that case a light rinse would have been sufficient.”

The book further stated:

“McCarthy’s press aides, appalled at the possible effects of this remark on Republicans, who, bereft of a dove candidate in their own party, might write-in McCarthy’s name, pleaded with reporters not to use it. They dutifully complied; though few would have done the same for Romney.”

While intriguing, American Melodrama doesn’t say when McCarthy made the comment, where, or specifically to whom.

Although self-censorship could account for the absence of contemporaneous references to McCarthy’s quip in leading U.S. newspapers, it seems implausible that an insult so delicious and devastating would have remained hushed up, even by compliant reporters, for very long.

Another version was offered by British journalist David Frost in an interview the aired on C-SPAN in 2007. Frost recalled having heard McCarthy’s comment, and said it was made in New Hampshire not long after Romney’s “brainwashing” statement.

But Frost’s recollection is faulty in a crucial respect: He said in the interview that “within a week or so” after making the “brainwashing” comment, Romney “was out of the race.”

Not so. Romney’s ended his campaign for the presidency on February 28, 1968 — six months after uttering the “brainwashing” remark and 3½ months after officially entering the race.

During the week Romney dropped out, Frost said in the C-SPAN interview, “I was interviewing Eugene McCarthy in New Hampshire, and, as we came out, there were three or four people who … wanted a sound bite. And one of them said, ‘What do you think about George Romney being brainwashed?’

“And McCarthy said, ‘I would have thought a light rinse would have been sufficient.’ Killer line. Fantastic line, I thought.”

But left unclear in Frost’s version is why journalists would have been asking McCarthy in late February or early March 1968 about a claim that Romney had made months before. Why would it have been newsworthy then?

Puzzling.

Not only that, but Frost did not say whether, or when, he reported McCarthy’s “killer line.” Or whether McCarthy’s “press aides” pleaded with him not to use it.